1. Field of Invention
The invention is a film, which has a rugged surface with tiny cilia, prepared by tetrapod-shaped zinc oxide nanopowders coated with a polymer including CFx and/or CHx functional groups. This transparent film possesses UV-shielding and water/oil repellent functions.
2. Related Art
Superhydrophobicity is exhibited by the unique microstructure and chemical properties of the leaves of certain plants in the nature. The characteristic of a superhydrophobic surface is that water forms spherical droplets immediately when dropping on the surface. Such a superhydrophobic surface possesses so-called “self-cleaning” function. For example, droplets formed on a lotus leaf carry the dust away by their rolling. This superhydrophobic phenomenon is caused by the roughness and low surface tension of the surface.
When a liquid drops on a surface of an object, an angle is then formed between the surface and the tangent line of the drop, called contact angel θ. When the tension in the gas-solid interface (also called solid surface energy) is high, the contact angle tends to be low, which means the surface easily gets wet. Contact angle of 0 degree indicates that water spreads over and becomes a film on the surface so that the surface would completely get wet. On the contrary, if the tension in the gas-solid interface is low, the contact angle tends to be high, indicating that the surface does not easily get wet. Therefore, contact angel of 180 degrees means that the liquid forms spherical droplets and cannot wet the surface at all.
When the surface with low surface energy is rougher, the contact angle would normally become higher. This is because the surface cavities with high aspect ratio may trap air so that the drop sits on a composite surface made of air and solid.
Presently, there are many methods for preparing a water-repellent surface. For example, U.S. Pat. No. 5,693,236 provides a water-repellent structure and its fabrication method including the steps of: preparing a mixture by mixing a curable liquid with a needle-like material; applying the mixture onto a surface of an object; curing a liquid of the applied mixture and forming an applied layer in which the needle-like material has been mixed on a base material of the cured liquid of the mixture; forming pits and projections of the needle-like material on a surface of the applied layer by etching the applied layer under a condition where an etching rate of the base material is larger than that of the needle-like material; and coating the surface of the applied layer with a water-repellent substance. The purpose of this invention is to provide a nanocoating material that is transparent and possesses superhydrophic and UV blocking properties.